Method and device for improving the transmission efficiency in a communication system with a layered protocol stack

ABSTRACT

In a method for improving the transmission efficiency in a communication system with a layered protocol stack, data packets are processed on an upper protocol layer. Data packets are forwarded to a lower protocol layer for transmission and the transmission is performed with variable channel access delays. The upper protocol layer is notified by the lower protocol layer when a transmission is started to allow a synchronization of timers in the upper protocol layer. If a layer performs a scheduling of data packets for the transmission, a rescheduling is performed alternatively or in addition during a channel access delay. Devices and software programs embodying the invention are also described.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for improving the transmissionefficiency in a communication system with a layered protocol stack,wherein data packets are processed on an upper protocol layer and areforwarded to a lower protocol layer controlling the transmission andwherein transmissions are performed with a channel access delay. Devicesand software programs embodying the invention are also described.

BACKGROUND

A communication system is generally specified using a layered approach.A layer either corresponds to a protocol or can be partitioned into twoor more sub-layers corresponding to a protocol each. Every protocol hasspecific responsibilities for the handling of information which isperformed by a specific set of functions and services for the protocol.A central idea behind dividing the functionality between protocols is toachieve a more understandable model of the system and hide details inthe different protocols to higher layers in the protocol stack.

An example of a mobile communication system in which layers aresubdivided into sub-layers or protocols is a WCDMA (Wideband CodeDivision Multiple Access) system according to 3GPP (3^(rd) GenerationPartnership Project) specifications. In this system, the data link layeris subdivided into the protocols PDCP (Packet Data ConvergenceProtocol), BMC (Broadcast/Multicast Control), RLC (Radio Link Control)and MAC (Medium Access Control) as described in 3G TS 25.301 V 3.4.0(3^(rd) Generation Partnership Project).

Information units denoted as primitives are exchanged between differentprotocol layers to communicate with each other. The primitives are usedin message sequence diagrams to illustrate the functional split betweenthe layers and how the protocols interact with each other when aspecific high level function is executed. A description of commoninterlayer service primitives and the interactions of different protocollayers can be found for the above protocols in 3G TS 25.303 V 3.3.0.

One example of a high level function is transmitting data betweenapplications using a random access channel. To perform this functionseveral protocols are involved. A random access channel (RACH) is awell-known concept for communication systems. Several users can transmitdata on a RACH independent of each other which results in a risk ofcollision between transmissions from or to different users. In order toreduce the probability of collisions and increase the probability ofsuccessful transmissions on a RACH certain transmission rules arespecified, especially waiting times delaying the transmission of data.One example of a waiting time is called a “back-off time” since the userbacks off from transmitting any information on the RACH for an intervalof time. Waiting times can vary in their length depending on controlparameters which are selected for example according to the number ofusers that use the RACH, i.e. the system load, or the interference levelfor a radio channel.

Generally, the protocol controlling the transmissions does not indicatethe duration of a channel access delay to other protocols which are thusunaware of how much delay is introduced before the transmission startson the RACH. In a communication system according to 3GPP specifications,the control of random access transmissions is executed in the MediumAccess Control (MAC) protocol as described in 3G TS 25.321 V3.3.0.

The channel access delay introduced before a transmission is started ona channel can vary considerably. This is a problem if the datatransmitted on a channel originates from a protocol comprising timers,for example an ARQ (Automatic Repeat Request) protocol that includesretransmission timers. It is difficult to set proper expiry values onsuch timers due to the large variance of the delay introduced by theprotocol layer controlling the transmission. A timer value can forexample be set too large according to some worst case delay, resultingin a slower retransmission time than necessary or according to a valuewhich is too small with a risk that the timer expires and an unnecessaryretransmission is performed.

Furthermore, new data will often become available for transmission inthe user equipment or a radio base station, e.g. in the RLC protocol,while the protocol controlling transmissions, e.g. MAC, is delaying atransmission of previous data. The additional data is sometimes timecritical while the transmission of previous data is less urgent. Whennew data is ready for transmission on a higher layer, e.g. on the RLCprotocol during a RACH procedure, it is not handled by the lowerprotocol, e.g. MAC, until the transmission procedure for the previousdata has ended, i.e. when the data is transmitted on the physical layer.For example if an SMS (Short Message Service) message is sent on theRACH this will delay higher priority data such as a call set-up messageuntil the RACH procedure for the SMS message is finished in the MACprotocol.

SUMMARY OF THE INVENTION

It is an object of the present invention to obviate the abovedisadvantages and provide methods which improve the control of channelaccess delays and the efficiency of data transmissions in acommunication system.

According to the invention, the method described in claim 1 isperformed. An alternative or supplementary embodiment is described inclaim 3. Furthermore, the invention is embodied in devices and programunits. Advantageous embodiments are described in the dependent claims.

A method is performed in a communication system with a layered protocolstack. Data packets are processed on an upper protocol layer and saidprocessing is performed according to at least one timer of the upperprotocol layer. The data packets are forwarded to a lower protocol layerfor transmission on a channel, wherein said transmission is controlledby the lower protocol layer. Additionally, the protocol stack cancomprise one or more further layers, e.g. a physical layer below thelower layer, the physical layer executing the transmissions, or a layerexecuting applications. The transmission is performed with variablechannel access delays which are caused for example by the controlprocedures or external conditions.

The start of a transmission is detected by the lower protocol layer.Generally an event, especially the sending of a primitive from the lowerprotocol layer to a physical layer, initiates the transmission on thechannel. If the period of time between event and transmission isdefined, it is often preferable to perform the detection of said event.When the start of the transmission is detected, the upper protocol layeris notified by the lower protocol layer of the starting time. At leastone timer of the upper protocol layer is synchronized according to thenotification. Especially, the notification can be sent at the start ofthe transmission and the timers can be started when the notification isreceived. If the transmission is started with an offset from a detectedevent, timers can be corrected by the offset.

Timers can be set according to actual transmission times and theinfluence of variable channel access delays removed. In this way theprecision of the timing and the control of the delays is significantlyenhanced and the efficiency of transmissions can be considerablyimproved.

The method is especially suitable for a timer which models a round triptime or a back-off time because the performance of the communicationsystem is sensitive to the correct setting of these timers. It ispossible that more than one corresponding timer is synchronized in thisway.

In a further method for improving the transmission efficiency in acommunication system with a layered protocol stack, data packets arealso processed on an upper protocol layer and are forwarded to a lowerprotocol layer controlling the transmission on a channel. Transmissionsare performed with a channel access delay and the upper or the lowerlayer performs a scheduling of data packets before the transmission. Inthe scheduling, data packets are reordered or priorities are attributedto data packets wherein the priorities determine which data packets aretransmitted with preference.

After the scheduling of the data packets is performed, channel accessdelays can occur. A channel access delay is detected on the lower layer.If necessary, the upper layer can be notified of the length or end ofthe channel access delay, e.g. by a corresponding primitive. A check isperformed whether additional data packets are ready for forwarding tothe lower layer at or before the end of the channel access delay. Thecheck can be performed for example by the upper layer or by the lowerlayer, especially if the latter performs the scheduling. If the trafficsituation has changed, i.e. if additional data packets are ready forforwarding or transmission at or before the end of the channel accessdelay, a further scheduling including the additional and the first datapackets is performed, i.e. the data packets are rescheduled fortransmission on the channel. If the lower layer performs the scheduling,the data packets or information about the data packets can be forwardedfrom the upper layer for this purpose. Finally, the data packets aretransmitted according to the rescheduling.

The proposed method avoids a blocking of time critical traffic by datapackets which were scheduled for transmission at an earlier time. Arepeated rescheduling is possible, especially in the case of anysubsequent channel access delay. Preferably, the rescheduling isperformed as close as possible before the transmission of data packetson a channel. The minimum period which is allowable between the start ofthe rescheduling and the start of the transmission is the processingtime necessary for rescheduling and preparing of the data packets fortransmission, which is determined by the processing speed of the deviceperforming the transmission.

In a preferable embodiment of the method, the scheduling is performed onthe lower layer. In this case, a notification can be sent from the lowerlayer to the upper layer requesting a transfer of additional datapackets or information about the additional data packets. The upperlayer transfers the information or additional data packets to the lowerlayer in reply to the request. In an alternative embodiment, the lowerlayer can access a memory which stores corresponding information fromthe upper layer.

Alternatively, the scheduling is performed on the upper layer. In thiscase, a notification of the channel access delay by the lower layerinitiates the further scheduling. The notification can include thelength or end of the channel access delay.

Preferably, protocols for an improved control of the delay in acommunication system embody both the above methods for synchronizingtimers and rescheduling data.

For the above methods, a notification is preferably sent at the start ofa transmission or the end of a delay, especially if the duration of adelay is arbitrary. This allows a simple embodiment of the proposedmethods. Alternatively, the notification can comprise a length of adelay before a transmission is started if the length is defined when thenotification is sent. This allows an increased processing time, e.g. forthe scheduling of data packets.

A total channel access delay can comprise two or more separatecomponents which are determined by different parameters or conditions,e.g. a random initial delay and an access delay. It is oftenadvantageous to perform a notification between the components,especially if the duration of the second component is arbitrary.

When the length of a component of the channel access delay is arbitrary,e.g. determined by a random parameter or external parameters which arenot controlled by the communication system, a suitable time for ascheduling or rescheduling is before the arbitrary delay component toensure sufficient processing time.

Preferably, a scheduling process is finished immediately before thescheduled data packets are transmitted, i.e. the delay between thescheduling procedure and the physical transmission is minimized.

The notification is preferably a primitive which can also be part of acommunication procedure consisting of two or more primitives.Information between different protocols can also be exchanged in otherways, for example using shared memories by two or more protocols.

The proposed method is especially suitable for a lower protocol layerwhich is a medium access control sub-layer of a data link layer, e.g.according to 3GPP specifications. A preferable upper protocol layer is aradio link control sub-layer of a data link layer.

The method is preferable if large variations in the channel access delayare possible. This is especially the case if the transmission isperformed on a channel which can be shared by several users and/or dataflows because transmission attempts may be unsuccessful due to accesscollisions or because mechanisms to avoid access collisions introducevariable delays. Examples are a Random Access Channel (RACH) or a CommonPacket Channel (CPCH) in the up-link from a user equipment to a basestation. A CPCH is defined in the 3GPP specifications for data packettransmission on a channel shared by several users. The method is alsoapplicable for down-link channels from a base station to user equipment,e.g. on a FACH (Forward Access Channel) or on a Downlink Shared Channel(DSCH) on which delays can vary due to traffic queuing.

A device in a communication system is adapted to perform at least one ofthe above methods. The device is for example a network node like a radiobase station for providing wireless access of user equipment to thecommunication system or a controller of a base station. The device canalso be a user equipment like a mobile phone, a personal digitalassistant or a laptop computer.

The proposed method can especially be embodied by a program unit on adata carrier or loadable into a device, e.g. a radio base station oruser equipment, in a communication system, the unit comprising code forperforming the steps of at least one of the above-described methods.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent in the following detaileddescription of preferred embodiments as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of devices in a communication system withdifferent protocol layers.

FIG. 2 shows the radio interface protocol architecture in acommunication system in the state of the art.

FIG. 3 shows a random access transmission sequence in a communicationsystem in the state of the art.

FIG. 4 shows a random access channel transmission control procedure inthe state of the art.

FIG. 5 shows a schematic random access control procedure according tothe invention.

FIG. 6 shows a random access transmission sequence according to theinvention.

FIG. 7 shows a detailed random access channel transmission controlprocedure according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1, devices in a mobile communication system are schematicallydepicted. A mobile communication system comprises radio base stations BSwhich provide access to user equipment UE by wireless connections WL anda core network interconnecting the base stations BS and providingconnections to further communication systems. Both user equipment UE andbases stations BS are provided with one or more transmitters andreceivers, generally combined into transceivers, to send and receivedata on a wireless connection WL. Connections CO of one or several radiobase stations BS to the core network are usually established via acontroller, e.g. a radio network controller (RNC) which is not shown tosimplify the drawing.

On every connection CO, WL, a protocol stack with layers correspondingto each other in the connected devices is defined. As indicated, not allupper layers need to be terminated in adjacent devices as information onsaid layers can be relayed to further devices. On the wirelessconnection WL, the protocol stack consists of five layers L1–L5. Thedata transmission is performed on the physical layer L1. Thetransmission is controlled by the data link layer L2. Above the datalink layer L2, the communication system in the example comprises anetwork layer L3 for radio resource control, a transport layer L4 and anapplication layer L5 for performing applications. Lower layers provideservices to higher layers while details how the execution of theservices is performed are generally not provided to the higher layers.The services are preferably executed by software programs run in aprocessing system of the base station and user equipment, respectively.Typically, a different protocol stack PS′ is used for the transmissionof data over the connection CO to the core network. Generally,information from several radio connections WL is multiplexed on a singleconnection CO to the core network.

FIG. 2 shows an example of subdivided layers in a communication systemwith a layered protocol structure as described in 3^(rd) GenerationPartnership Project specification 3G TS 25.301. Embodiments of theinvention are described using this system as an example although theinvention is not restricted to a WCDMA system and can be applied to anycommunication system with a layered protocol stack if the system haschannel access delays and timers controlling the transmission orperforms a scheduling of data packets.

In FIG. 2, the data link layer L2 between the physical layer L1 and thenetwork layer L3 with the radio resource control RRC is subdivided andcomprises the protocols PDCP, BMC and MAC. Higher layers control thefunctionality in lower layers as indicated by lines. The functionalityof some layers, e.g. PDCP, is only attributed to selected connections.In the protocols PDCP and RLC (radio link control), separate functionentities are attributed to different connections. As indicated by theoval shapes, interfaces allow a redistribution of information betweenconnections on the different layers.

The protocol RLC is an ARQ (Automatic Repeat Request) protocol and afurther sub-layer of the data link layer L2. Timers are part of the ARQfunctionality and are started when RLC packet data units are transferredto the MAC protocol layer for further transfer to the physical layer.Since the delay introduced by MAC between the reception and furthertransfer of packet data units can vary considerably, it is impossible toset the timers in RLC to optimal values. The delay introduced beforetransmission on a channel can also depend on external parameters. Forexample, RACH load control parameters like the persistence value in acommunication system according to 3GPP specifications are broadcast bythe radio network nodes, e.g. base stations, to adapt delays to thepresent interference level or to the present load of the communicationsystem and avoid congestion.

FIG. 3 shows service primitives sent between the involved protocols whenRLC packet data units are transmitted from a user equipment on therandom access channel in a WCDMA system in the state of the art. Detailsof the depicted primitives, messages and interfaces are described in 3GTS 25.303. The wireless connection between user equipment UE and basestation BS is performed over the interface 18 Uu while the connectionbetween base station and the controller RNC corresponds to the interface19 lub. The part left of the interface Uu in FIG. 3 describes thehandling of data within the user equipment.

For the initiation of a transmission between the user equipment and abase station, upper layers at first perform a configuration of lowerprotocol layers by corresponding primitives 20, 21. Then, the primitive22 “MAC-Data-Req” transfers data packets for transmission from the RLCprotocol to the MAC protocol. Furthermore, the time of sending primitive22 “MAC-Data-Req” is used in the state of the art to start timers withinRLC although the transmission on the Uu interface 18 is not starteduntil a message 30 “RACH Data”. Before message 30, an initial back-offtime 24 elapses. A further delay 25 is due to the channel accessattempts that are performed repeatedly with increasing power until asuccessful reception of a transmission header is confirmed by the radiobase station BS with an acknowledgement 28. Still further delays may becaused by one or more subsequent back-off times 26 with correspondingaccess delays 27 if the first access attempt was unsuccessful, e.g.rejected by a negative acknowledgement 29. As a result, typical totalchannel access delays between the primitive “MAC-Data-Req” 22 and thetransmission of the packet data units on the RACH from the userequipment to the radio base station with the message 30 “RACH Data” canvary between 10ms and 1.5s with even higher values possible in congestedsituations.

FIG. 4 shows the corresponding flow chart for the transmission controlprocedure in the MAC protocol as described in detail in 3G TS 25.321.After configuration 40, checks 41 are performed by the MAC protocolwhether data packets are ready for transmission. If this is the case, ascheduling according to the priority of the data packets is performed instep 42. Furthermore, a variable access back-off delay is enabled byassigning a constant P_(i) to data packets or groups of data packets iin step 43. A loop 44 is entered which delays the channel access for arandom time to avoid access collisions. To accomplish a statisticaldistribution of accesses, a random number is calculated and compared tothe constant P_(i) attributed to a data packet or group of data packets.Loop 44 which corresponds to the initial back-off time is ended when therandom number is smaller than or equal to constant P_(i) while else afurther random draw is performed after a waiting period. By transmittinga message to initiate an update 45 to change allowed ranges for theconstant P_(i), the network is able to control the load on the randomaccess channel.

After the initial back-off delay, access attempts are performed asdescribed with respect to FIG. 3. In case of a successful attempt, thedata is forwarded to the physical layer for transmission to the basestation in step 50. Else loop 44 is again entered after a waiting time46, 48. Different lengths of the waiting time 46, 48 can be specified ifthe user equipment can distinguish different reasons for an unsuccessfulaccess. A counter M ensures an error handling if a specified number ofaccess attempts was unsuccessful.

The proposed methods comprise two basic parts which are both depicted inFIG. 5. In a first part, different protocol layers within a userequipment are synchronized so that timers are not started too early orlate when a transmission of data is delayed. The start of the timers issynchronized with the actual transmission of data on a channel, e.g. arandom access channel. The corresponding communication system includes afirst protocol, e.g. RLC, with timers determining the processing of databy the first protocol. Other protocols, e.g. MAC, add delays beforeprotocol data units generated by the first protocol are transmitted on aphysical channel in the communication system. The start of timers in thefirst protocol is synchronized with the event that the data istransmitted on the physical channel.

Said first part improves the interlayer communication, for examplebetween the physical layer, MAC and RLC in a user equipment. It enableshigher layers to consider delays caused by lower layers, e.g. allows toMAC and RLC to react to changes in the random access delay. Theindication to start timers is performed upon successful channel accesswhich avoids variations and inaccuracies caused by the delays, e.g. in arandom access procedure.

In a second part, a rescheduling of data ready for transmission on achannel is performed when additional data becomes available. Thecorresponding communication system includes a protocol, e.g. MAC, thatperforms the scheduling of data units for transmission. If transmissionson the channel are delayed, e.g. due to access attempt delays orback-off times, rescheduling of additionally received data is performedby said protocol before previously received data is transmitted. Thesecond part enables the protocol to perform rescheduling especiallyduring a random access control procedure when the traffic situation haschanged.

Both parts are illustrated in the schematic block diagram of FIG. 5which comprises components of a typical random access procedure for auser equipment in the protocol controlling the transmission, e.g. in theMAC sub-layer of the data link layer. Random access procedures in amobile communication system typically consist of several components, allcontributing to the total delay that packets from higher layerexperience during the procedure. Details of the access procedure canvary depending on the communication system considered.

After data packets are forwarded from a higher layer in the protocolstack in step 60 for transmission, an initial back-off delay 64 spreadsrandom access attempts in time to minimize the collision probabilityduring the channel access phase when more than one user equipment usesthe same random access channel. The length of initial back-off delay 64is variable following a statistical distribution, e.g. due to a loop 44as described above, and parameters influencing the length of the delaycan be varying in time. The subsequent access attempt delay 65corresponds to the time required to access the random access channel.For instance in a communication system applying Carrier Sense MultipleAccess (CSMA), access attempt delay 65 preferably corresponds to thecarrier sense phase, in which the channel is sensed for ongoingtransmissions from other parties. In a communication system using powerramping, access attempt delay 65 preferably corresponds to the powerramping phase. The power ramping adapts the transmission power of userequipment to the present channel conditions and consists of subsequentpreamble transmission attempts with increasing power. When a sufficientpower level is reached, i.e. when the preamble is successfully receivedby a radio base station, the network acknowledges the preamble. Thereception of the acknowledgement ends the access attempt delay 65.

When an access attempt during the access attempt delay 65 is successfulas detected in check 70, the transmission 74 of the data on a physicalchannel is performed. If the result of check 70 is that a channel accessattempt has failed, the protocol falls back into a subsequent back-offdelay 66, 68. In FIG. 5, the protocol distinguishes different reasonsfor a failed attempt in further check 71 and the duration of thesubsequent back-off delay 66, 68 depends on the reason for theunsuccessful channel access. When the user equipment does not receive anacknowledgement from the network confirming a successful channel access,the subsequent access is delayed by a certain amount of time asindicated by “Subsequent Backoff Delay 1” 66. If a negativeacknowledgement as an indication of congestion is returned from thenetwork, the user equipment uses a longer “Subsequent Backoff Delay 2”68 to ease the load on the channel. Additional reasons corresponding tofurther subsequent back-off branches are possible.

When timers in a higher layer of the communication system are startedwith forwarding step 60, the starting of the timers may differsignificantly from the time of the physical transmission 74 due thevariable and often unpredictable lengths of delays 64–66, 68. Therefore,it is proposed that the depicted protocol layer informs a higherprotocol layer close to the time of the physical transmission 74 in step72, e.g. by a primitive, when the data is forwarded to the physicallayer after check 70 indicated a successful access attempt. In this wayit is ensured that the timers are started at the time of transmission.If a processing time is necessary for the data packets between check 70and transmission 74, the length of the processing time is constant andcan therefore be considered in setting timers and it is generally smallcompared to the delays 64, 65.

In one embodiment, the proposed rescheduling 69 a is performed after theinitial back-off delay 64. The user equipment is not in control of theduration of the access attempt delay 65 which is determined as describedabove by transmission conditions or behavior of other users of thecommunication system and therefore generally unpredictable.Implementation reasons can require to perform the rescheduling a periodof time before transmission 74. For example, for a communication systemaccording to 3GPP specifications, transmission 74 is specified to startwithin a limited period after an acknowledgement by the networkindicates a successful access attempt. This period is not alwayssufficient for data packet processing. Therefore, a suitable time forthe rescheduling 69 a is before access attempt delay 65 to providesufficient time for the user equipment for packet processing like forexample channel coding, interleaving or cyclic redundancy checkcalculation.

However, a rescheduling at any time during the channel access delay,i.e. between step 60 and transmission 74, can improve the performance ofthe communication system. Examples are rescheduling 69 b, 69 c which maybe performed alternatively or in addition to rescheduling 69 a. It ispossible to reschedule once or more than once and at any time during thechannel access delay. It is preferable to perform a rescheduling asclose as possible before transmission 74. For a sufficiently highprocessing speed of the data packets, the preferred time of therescheduling coincides with step 72 immediately before transmission 74.

It is possible, that data which is to be transmitted on a physicalchannel is grouped into different access classes. Access classes cancorrespond for example to data of users with different subscriptionscorresponding to different quality-of-service classes to which a user isentitled. In this case, parameters which determine the duration of adelay 64–66, 68 can differ between the access classes. An improvement ofthe performance can be achieved by allowing a rescheduling between dataof different access classes. In other situations it may be advantageousto allow a rescheduling only within a current access class or between asubset of access classes. Different rules for a rescheduling can applyat different times during the channel access delay. Especially, it ispossible that a change of the access class is not allowed for arescheduling at step 72 while it is possible for a rescheduling 69 a–69c.

In a random access transmission sequence according to the proposedmethods, two new primitives are introduced which are denotedMAC-Re-Schedule primitive 100, 104 and MAC-Data-CNF primitive 108.Primitives 100, 104 MAC-Re-Schedule are used by MAC to requestadditional data from the RLC protocol. The primitive can for example besent after a rescheduling has been performed or in order to trigger arescheduling. The primitive 108 MAC-Data-CNF is used by MAC to informRLC that the random access control procedure is finished and thetransmission of a set of packets has started. RLC uses the reception ofprimitive 108 as trigger to start timers.

FIG. 6 depicts how the primitives 100, 104, 108 can be used to improvethe random access procedure in a WCDMA system. After a transmissionbetween the user equipment and a base station is initiated and lowerprotocol layers are configured, the primitive 82 “MAC-Data-Req”indicates to the MAC protocol that one or more RLC protocol data unitsare ready for transmission. After subsequent initial back-off time 84,additional data with higher priority may be available on RLC. In apreferred embodiment, MAC has access to information on the buffersituation of RLC, for instance by a shared memory area. Based on thisinformation, MAC makes a rescheduling decision in which both the datapackets originally scheduled for transmission and the additional dataare considered. MAC then informs RLC with the primitive 100 that it hasmade the rescheduling and that RLC shall prepare the data fortransmission according to the rescheduling. The preparation consists ofe.g. setting fields in the header of the RLC protocol data unit. Whenthe RLC protocol data units are ready, RLC replies to primitive 100 withthe data for transmission according to the rescheduling in primitive 102“MAC-Data-Req”. Persistence value constants P_(i) assigned to data canbe changed after the rescheduling.

A corresponding dialogue with a further rescheduling can be performedafter any subsequent back-off time 86 with exchange of a furtherMAC-reschedule primitive 104 and a further MAC-Data-REQ primitive 106.It should be noted that the subsequent back-off time 86 can comprisedifferent components, e.g. both an initial back-off delay 64 and asubsequent back-off delay 66, 68 as described with respect to FIG. 5.When the MAC protocol layer receives the primitive 89 PHY-Access-CNFindicating the start of the actual transmission, MAC uses theMAC-Data-CNF primitive 108 to inform RLC to start timers. In this way,erroneous timer settings due to the variable back-off times 84, 86 andaccess delays 85, 87 can be avoided because the offset between theprimitive 89 PHY-Access-CNF and the transmission of the data on thephysical channel with the message 90 RACH data is constant andpredefined.

It should be noted that a rescheduling is possible at any time betweenprimitive 82 MAC-Data-Req and primitive 109 PHY-Data-Req, e.g. initiatedby a communication procedure with primitives 100, 102. If the device hassufficient processing speed to perform the data handling in time for thesending of the message 90 RACH data which must, according to 3GPPspecifications, be performed in a specified interval after reception ofthe acknowledgement 91 of a channel access, it is preferable to performthe scheduling close to sending the primitive 109 PHY-Data-Req. Forexample, primitives 100, 108 could be sent almost simultaneously in thiscase.

Several alternative embodiments of the invention are possible.Especially, the rescheduling can be performed by the RLC protocol. Inthis case, the primitives 100, 104 request the rescheduling by the RLCprotocol and rescheduled data is transmitted with primitives 102, 106.Different alternative options are applicable for this case:

-   -   The RLC protocol can send additional data only if the priority        is higher than that of the previous data. In this case, the MAC        protocol queues the previous data and forwards the additional        data with higher priority. Alternatively, the MAC protocol        discards the previous data and the RLC protocol marks the        previous data as not sent in the RLC transmission buffer.    -   The RLC protocol can send to the MAC protocol both the        additional data and the original data with the rescheduled        priorities. Then the original data packets stored by the MAC        protocol are deleted.

FIG. 7 shows an improved RACH transmission control procedure for analternative embodiment compared to the method depicted in FIG. 6. TheMAC rescheduling and triggering of RLC timers is amended compared toFIG. 4 while the other elements in FIG. 7 correspond to those in FIG. 4.After the initial back-off delay in loop 110, a check 112 is performedwhether a MAC rescheduling is necessary, e.g. a primitive is sent to RLCto request additional data which is ready for transmission and thereception of a reply with additional data in a primitive is waited for.If additional data packets are received, a rescheduling 114 of the datapackets is performed. Additionally, new constants P_(i) may be assignedto the data packets in step 113 and optionally the parameter M can bereset. The MAC-Re-Schedule primitive is sent in step 115. At a definedtime with respect to the initiation of the transmission of data packetson the physical layer by the primitive PHY-DATA-REQ 118, preferablysimultaneously to or immediately before or after the sending ofprimitive 118, the MAC protocol sends a MAC-Data-CNF primitive 108 instep 116 to the RLC protocol. The order of the steps 113, 115 andrescheduling 114 in the previous description can vary, e.g. depending onwhich protocol performs the scheduling. Furthermore, a reschedulingcheck 112 can be performed at any other time in FIG. 7 between theinitial scheduling and the sending of the MAC-Data-CNF primitive in step116.

The primitives depicted in FIGS. 6, 7 do not necessarily illustrate asingle transfer of information but can also correspond to acommunication procedure instead. A depicted primitive can represent anexchange of information between protocols in both directions.Information between protocols can also be exchanged by access to amemory which is shared by two or more protocols. For example, any of theprimitives 100, 104 MAC-Data-Req, primitives 102, 106 MAC-Re-Schedule orprimitive 108 MAC-Data-CNF can include an exchange of information on RLCbuffer levels, changes in RLC buffer levels or transport channelparameters. In this way, information can be exchanged on, e.g., thenumber of data packets which can be transferred. Correspondinginformation exchange between the protocols is also possible at othertimes during the channel access delay, e.g. triggered by the arrival ofadditional data at the RLC protocol or changes of parameters of thephysical channel.

RLC timers are very sensitive to changes in round trip time and onlywith an exact value it is possible to configure RLC in an optimum wayfor RACH transmissions. The transmission in the reverse direction, i.e.in the down-link from base station to user equipment, is generallyperformed on a Forward Access Channel (FACH). The proposed methods allowto set the RLC timers according to the actual transmission time. The RLCround trip time then depends only on the variable Forward Access Channelscheduling delay in the down-link. In the state of the art itadditionally depends on the variable RACH access delay in the up-link.Therefore, one of two variable contributions to the round trip time isremoved and the estimation of the round trip time improved.

By checking before the channel access whether additional data is readyfor transmission, rescheduling of data according to priorities at themoment of transmission is possible. This allows to give priority toimportant RLC packet data units close to the actual transmission timeand avoid situations in which important traffic is delayed by lessimportant traffic.

The proposed methods can be used both in a communication system withFrequency Division Duplex (FDD) and with Time Division Duplex (TDD).

The above embodiments admirably achieve the objects of the invention.However, it will be appreciated that departures can be made by thoseskilled in the art without departing from the scope of the inventionwhich is limited only by the claims.

1. A method of improving transmission efficiency in a mobilecommunication system with a layered protocol stack, the methodcomprising: processing data packets on an upper protocol layer;controlling the processing according to at least one timer provided onan upper protocol layer; forwarding the data packets to a lower protocollayer for transmission; controlling the transmission by the lowerprotocol layer; transmitting the packet by a physical layer that isdifferent from the lower protocol layer; initiating a transmission witha variable channel access delay caused by a control procedure of thelower protocol layer; detecting the start of a transmission by the lowerprotocol layer; notifying the upper protocol layer by the lower protocollayer when a transmission is started; and synchronizing the at least onetimer of the upper protocol layer according to the notification.
 2. Themethod of claim 1, wherein the timer models a measure of time selectedfrom the group consisting of a round trip time and a back-off time. 3.The method of claim 1, wherein a notification is sent at the start of atransmission or at the end of a delay.
 4. The method of claim 1, whereina total channel access delay comprises at least two separate componentsand a notification is sent between the at least two separate components.5. The method of claim 4, wherein the channel access delay includes acomponent of arbitrary length and at least one of a notification and ascheduling is performed before the component of arbitrary length.
 6. Themethod of claim 1, wherein a scheduling process is finished immediatelybefore the scheduled data packets are transmitted.
 7. The method ofclaim 1, wherein a notification is a primitive.
 8. The method of claim1, wherein the lower protocol layer is a medium access control sub-layerof a data link layer.
 9. The method of claim 1, wherein the upperprotocol layer is a radio link control sub-layer of a data link layer.10. The method of claim 1, wherein the transmission is performed on achannel that can be shared by at least one of a plurality of severalusers and data flows.
 11. A device in a mobile communication system,comprising: a layered protocol stack, adapted to process data packets onan upper protocol layer and control the processing according to at leastone timer provided on the upper protocol layer; the layered protocolstack further adapted to forward the data packets to a lower protocollayer for transmission and to control the transmission by the lowerprotocol layer; the layered protocol stack adapted to facilitatetransmission of the data packets by a physical layer that is differentfrom the lower protocol layer; a means for initiating a transmissionwith a variable channel access delay caused by a control procedure ofthe lower protocol layer; a means for detecting the start of atransmission by the lower protocol layer; a means for notifying theupper protocol layer by the lower protocol layer when a transmission isstarted; and a means for synchronizing at the least one timer of theupper protocol layer according to the notification.
 12. The device ofclaim 11, comprising at least one of a user equipment and a networknode.
 13. The device of claim 11, wherein the at least one timer isadapted to model at least one of a round trip time and a back-off time.